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When irradiated with electrons or γ-rays, a number of biological molecules display an approximately linear relationship between the reciprocal of the D37 dose and molecular weight. This is conventionally plotted as a relation between target molecular weight and true molecular weight, where the target molecular weight Mt is given as: Mt × (D37) = α (1) where α is approximately 1010 Da-rad/eV of the energy assumed to be “deposited in the target” in a single “hit” for expression of the end-point. We emphasize that D37 is expressed in rads for we will later write d37 as having the same connotation but expressed in erg/g. The difference between the two is simply a factor of 100, but the use of two different symbols makes for a smoother presentation. As a reminder, the D37 dose is the dose, in rads, at which there is 37% survival of the target molecules irradiated by γ-rays. Different authors (Hutchinson and Pollard, 1961; Dertinger and Jung, 1970; Alper, 1979) estimate the required energy deposition to be about 60 or 75 eV. See the references for the details of the calculations and for plotted relationships between the target molecular weight and the true molecular weight.